A measurement of the rate of type Ia supernovae at redshift z ∼ 0.1 from the first season of the SDSS-II supernova survey

We present a measurement of the rate of Type Ia supernovae (SNe Ia) from the first of three seasons of data from the SDSS-II Supernova Survey. For this measurement, we include 17 SNe Ia at redshift z ≤ 0.12. Assuming a flat cosmology with Ω_m = 0.3 = 1 - Ω_Λ, we find a volumetric SN Ia rate of [2:93_-0.040 ^+0.17(systematic)_-0.71^+0.90(statistical) × 10^-5 SNe Mpc^-3 h₇₀³ yr ^-1, at a volume-weighted mean redshift of 0.09. This result is consistent with previous measurements of the SN Ia rate in a similar redshift range. The systematic errors are well controlled, resulting in the most precise measurement of the SN Ia rate in this redshift range. We use a maximum likelihood method to fit SN rate models to the SDSS-II Supernova Survey data in combination with other rate measurements, thereby constraining models for the redshift evolution of the SN Ia rate. Fitting the combined data to a simple power-law evolution of the volumetric SN Ia rate, r_V ∝ (1 + z)^β, we obtain a value of β = 1.5 ± 0.6, i.e., the SN Ia rate is determined to be an increasing function of redshift at the ∼-2.5 σ level. Fitting the results to a model in which the volumetric SN rate is r_V = Aρ(t) + Bρ(t), where ρ(t) is the stellar mass density and ρ(t) is the star formation rate, we find A = (2.8 ± 1.2) × 10^-14 SNe M_⊙^-1 yr ^-1, B = (9.3-_3.1^+3.4 × 10^-4 SNe M_ȯ^-1.